The present invention relates to a touch sensor which is used as a measuring device, and particularly to a touch sensor which is used to examine the machining accuracy of worked products or is used in a numerical control tool machine with an automatic tool converter (ATC) known as the machining center. This touch sensor may be housed in the tool magazine of said machining center when it is not in use and is attached to the spindle when required after being taken out from the magazine with a manipulator, then the headstock is moved properly to make a contact directly with the workpiece and the position to be worked, for example, the distance to the end face to be worked, the size of the hole to be worked and so on are detected and finally the detecting signals are sent to the control device.
Conventionally, various types of touch sensors of this kind have been proposed. A typical structure of those touch sensors is such that a sensor rod is held at a definite position only with a spring means, the sensor rod is displaced against said spring means when the sensor rod has contacted the workpiece, and the displacement signal is detected with a sensing device.
Holding the sensor rod only with a spring means in this way will bring about difficulties in displacing and operating the sensor rod exactly. As a result, it will be difficult to detect the exact position to be worked of the workpiece.
Therefore, the first object of the present invention is that not only holding the sensor rod at a definite position on the casing in such a manner that the rod is centered very exactly, but also detecting exactly the position to be worked of the workpiece having the sensor rod displaced sensitively and exactly when the sensor rod has contacted to the workpiece.
The second object of the present invention is to provide a touch sensor wherein not only the shock generated when the sensor rod contacts to the workpiece is alleviated to prevent the sensor from breaking or failing, but also both conductive and non-conductive workpieces are used and yet the mounting and operating of the sensor may be easy.